Radio system



Aug. 7, 1945. c. w. HANSELL RADIO SYSTEM 2 Sheets-Sheet 2 Filed Dec. 27,1940 INVENTOR CLARENCE W IVSELL BY 7% ATTORNEY Patented Aug. 7, 1945RADIO SYSTEM Clarence W. Hansell, Port Jefferson, N. Y., assignor toRadio Corporation of America, a corporation of Delaware ApplicationDecember 27, 1940; Serial No. 371,865

41 Claims.

The present invention relates to-improvements in radio communication,and has for its primary object to improve the signal-to-noise ratio ofradio systems. A further object is to obtain the aforesaid improvedsignal-to-noise ratio without increasing the size of the vacuum tubeequipment furnishing the power to the radio transmitter.

The inventicn is primarily applicable to radio systems for thetransmission and reception of telegraph signals, including printersignals, and may also be used for the transmission and reception ofslowspeed facsimile signals.

The objects of the present invention are achieved, in brief, byradiating from the transmitter short pulses of increased power (i. e.,increased relative to the permissible steady state value) andconditioning the receiver to be responsive substantially only during theintervals when energy iscoming in from the transmitter. At thetransmitter, the output power is continuopsly stored and then used forshort time periods to produce pulses or bursts of power. By radiatingallthe stored output power in relatively short periods of time comparedto the intervals between radiation periods, there is obtained anincreased power output comparedt'o a normal steady state value of poweroutput. The normal steady state value is the power output which thetransmitter can deliver continuously. At the receiver, the responseperiod is timed synchronously with the transmitter so that the receivergives an output which is caused only by the energy present at the timesignal energy is coming in from the transmitter. To achieve this, thereceiver is blocked or quenched at some point, or points, ahead of thosecircuits which effectively contribute to the receiver selectivity,

We can consider the signal-to-noise power ratio in radio circuits asratios of energy flow per unit oi time. In general, the total noiseenergy in the output of a receiver is proportional to noise powermultiplied by time. If the time during which a receiver is operative isreduced to 16%, the total noise energy and average power in the outputof the'receiver will alsobe' reduced to 16%. Thatis, a receiver which iscontrolled in such a way as to be responsive during intervals of [3mm ofa second repeated at a rate of 590 cycles, will have. a: noise initsoutput reduced by about ten to one in power. If the repetition rateis reduced to 50, still maintaining /5000 second as the responsiveperiod of the receiver, the noise power, or energy rate, in the outputof the receiver will be reduced by one hundred to one.

This reduction in responsive time at the receiver will be of no value inimproving signalto-noise ratio when used on an ordinary signal becausethe useful signal will be reduced in the same ratioas the noise.However, by storing up the output power from the transmitter and thenradiating it all in a second bursts at times synchronous with thereceiver responsive period and with correct timing between transmitterand receiver so that the signals arrive at the receiver when it isresponsive, then there can be obtained an improvement in signal-to-noiseratio. This is generally what is done in the present invention.

If, for example, we have a transmitter which has an available output ofabout 200 kilowatts,

whereby any noise which exists between periods of signal input to thereceiver is prevented from contributing to noise output from thereceiver. In this way, no noise is permitted to build up energy in theselective circuits of the receiver exceptthat' which exists while thereceiver circuits are receptive or open. During these open periods ofthe receiver, the signal, with its increased power, makes its greatestimpression.

In order that the present invention may be better understood, anexplanation of the theory underlying the invention will now be given.While this'explanation is believed'to be correct, it is not of"necessity complete, nor does the operation of theinvention depend uponits accuracy or otherwise.

and the transmitter power output were stored up and. then used during ofa second intervals, repeated at a 500 cycle rate, then thesignal-to-noise ratio would be improved as though the transmitter powerhad been increased from 260 kilowatts to 2000 kilowatts. By storing upthe transmitter power output, we are, in efiect, enabled to release atthe pulse period a power output which in fact greatly exceeds the normalsteady state value of an ordinary signal. If the pulse period is its ofthe total time used for transmission, then theoretically it is possibleto send out during pulse periods or ten times the power output of thesteady state signal. This is because the rate of change of stored energywhen being transmitted during pulse periods is very much greater thanthe rate of change of stored energy during off periods when thetransmitter is delivering power to the storing oscillatory circuit. If,in the immediately foregoing example, the repetition rate were reducedto 50 cycles, then the power output during the active periods would beequivalent to 20,000 kilowatts. By employing circuits having suitableantenna power gains due to the use of a directive antenna, it ispossible to still further increase the signal-to-noise ratio. An antennapower gain of 100 to 1, for example, would increase the effective powerto 2,000,000 kilowatts.

Although at first blush it might be thought that a timed spark typetransmitter would provide a signal with high peak amplitudes more orless equivalent to the type of signal necessary to obtain the benefitsof the present invention, it is believed that such a transmitter is notpractical for high power because the physical dimensions of theequipment required for a high power with spark transmission make highfrequency operation impractical. Further, spark generators, generallynecessary in the spark type transmitter, lose efiiciency at very highfrequencies due to time lags in break down of the air in the spark gaps.Under some circumstances, however, it might be possible to use a timedspark type transmitter, although such an arrangement is not preferred tocarry out the purposes of the invention. According to the presentinvention, it is proposed to employ low power factor oscillatingcircuits for storing energy in the transmitter. Such circuits may be ofthe concentric resonant line type now well known in the art. They mayalso be resonant metal enclosed cavities, known as cavity resonators.These low power factor circuits may be fed with energy continuously froma continuous wave transmitter during periods when transmission isdesired, and energy for the antenna may be drawn from these low powerfactor circuits during short time intervals at a rate considerablyhigher than the transmitter could deliver directly. As an illustration,it is practical to obtain resonant line low power factor circuits withthe power factor due to losses in the line itself of about one part in20,000 (Q:20,000). Of course, dif ferent and higher values of Q areattainable with special design of the circuit elements.

The following is a detailed description of the invention accompanied bydrawings, wherein:

Fig. 1 illustrates in abbreviated form the essential circuit elements ofa transmitter for transmitting short pulses of energy in accordance withthe principles of the invention;

Figs. 2 and 2a. are details showing two different forms of the tootheddisc wheel which can be employed in the transmitter of Fig. l; and

Fig. 3 illustrates the principles of the invention applied to a completeradio communication system having a transmitter and a receiver.

Referring to Fig. 1, there is shown a high frequency radio telegraphtransmitter l Whose output is fed to the transmitter output coil I! fromwhich energy is passed through half wavelength line sections 3, 3 to ahalf wavelength resonant line 4. Output from the half wavelengthresonant line 4 is supplied to the antenna 1 through variable couplingcondensers provided by plates 5, 5 in cooperation with a toothed wheelor disc 6 and also through coils H and transmission line l2. Transmitteri and its output coil ll are surrounded by a grounded metallic shieldl5, while the half wavelength line sections 3, 3 and the half wavelengthresonant line 4 are respectively shielded by means of surroundingshields i6 and 13. The line sections 3, 3 are each one-half wavelengthlong as measured from the points of connection on the output coil H tothe points of connection on the half wavelength resonant line 4.Obviously, the electrical length of the line has been referred to, sincethe physical length may be something more or less than this, due to endeffects and so forth. The connections of the line sections 3, 3 to thecoil l1 and to the resonant line 4, are, it should be noted,symmetrically arranged with respect to the center or nodal points onthese elements. Similarly, the connections from the resonant line 4 tothe condensers constituted by the plates 5, 5 are also symmetricallyarranged and on opposite sides of the mid point or nodal point on theresonant line.

The toothed disc 5 is driven by means of a hub l0 and a shaft 0connected to a motor (not shown), at an exact speed, which may be doneby controlling a synchronized driving motor, to which the shaft 9- islinked, from an extremely accurate frequency standard. This is describedin more detail in connection with Fig. 8. This toothed disc is madeprimarily of insulation and has metal teeth symmetrically arranged onopposite sides of the shaft and may take any one of the forms indicatedin Figs. 2 and 2a. Each tooth in the disc 6 is a desired percentage, letus say somewhat less than 10%, oi the total distance around theperiphery. When one metal tooth is between the plates 5, 5 of onecondenser, the other metal tooth will be between the plates 5, 5 of theother condenser on the opposite side of the wheel 6, Thus, thesecondensers 5, 5 have maximum capacity when a metal tooth happens to bepositioned between the plates, and at this time will permit the deliveryof near maximum output from the half wave resonant line 4 to theantenna 1. For low values of capacity of the condensers 5, 5, the outputis made very low. It will thus be noted that the capacity of thesecondensers is varied by means of the toothed wheel 6 which is sodesigned and operated that power is fed to the antenna for shortperiods, let us say, of 1 second repeated at intervals of of a second.Both condensers will have maximum capacity simultaneously, and alsominimum capacity simultaneously.

The variable inductors 8, in parallel to the condensers, serve toneutralize the residual capacity of the condensers when no signal orradiation desired, which will occur between pulses or during idleperiods corresponding to the time when spaces between the metal teeth onthe wheel or disc 6 are present between the condenser plates. The coils8, 8 are adjusted to give the minimum current in the antenna duringthese no signal or off periods.

Coils H, ll are provided in series with the conductors of the feed lineH. in order to tune out the reactance of the condenser and coil systom5, 3 when the condensers have a maximum capacity. That is, the coils II,II provide a series short circuit in the transmission line leads (i. e.,minimum impedance therein to energy of the operating frequency) toenable maximum current to go to the antenna from the half wave resonantline '4. i

If the-transmitter l were capableof delivering 200 kilowatts, givenbyway of example only, then the antenna load, when it is effective,should be able to take up to 2000 kilowatts. The three half wave linesections 3, (land 4 serve as a fiy wheel, so to speak, or tank circuitto smooth out the load fluctuations and thereforehold substantiallyconstant load on the transmitter I.

' 'lhe toothed wheel condenser arrangement, in order to handle thelargeamount of power re-' quired, should preferably be operated in compressedair or in a compressed gas, such as hydrogen, helium, nitrogenjczirbondioxide, etc., which should prevent oxidation in case of arcing betweencondenser plates. If thepressure of the compressed gas be madeto be 1500pounds or about 100 atmospheres, the'spa'cing between the elements inthe condenser might be reduced to something like 1% or less of thatpermissible in open air before there occurs the danger of arcing.Consequently, for a given capacity, the area of the condenser plates canbe reduced to 1% of that required in open air. Thus, at '100 atmospheresof the total'volume required'for the working part of'the condenser'wouldbe only of that which would be'required in openair. To reduceradiationdue to residual or minimum capacity inthe variable condenser, there maybe used, if desired, capacity balancing or neutralizationcondensers'(criss-cr-oss arrangement) between: the condenser plates, as is'commonly used in push-pull amplifier circuits fora similarpurpose,instead of tuning out the residualcapacity by means of the coils 8, 8,to form with it an antifresonant circuit: as shown in Fig. l..

v Fig. 3"shows in conventional box form a complete radio systemoftransmitter and receiver embodyingthe principles of the present inventionj The transmitter is. designed in a manner shown in Fig. lto'radiateshort' 'pulses,or bursts of signal power from antenna lfl The toothedwheel or disc 6 in the transmitter is linke'd by means of its shaft 9,anda speed changing gear if necessary, to a synchronized driving motor20, in turn controlled through a frequency divider 2| bya crystaloscillator 22. Oscillator)!- is an extremely accurate frequency standardwhich generates, by way of example, oscillations of 100,000 cycles. {Thefrequency divider, coupled to the output of the crystal oscillator overcircuit 23, may reduce the frequency of the crystal oscillator to afrequency of, let us say, 50 cycles which can then be applied tothemotor 20 over circuit 24. In thisway the motor it} is driven at anexact speed. n V

The receiver includes a suitable antenna 26 which feeds the collectedsignal. energy to a suitable radio frequency amplifier stage .and thento a heterodyne and detector stage 2'1, from which intermediatefrequency energy is applied to a keyed amplifier stage. 28. Oscillator3! is. ,a

heterodyne oscillator for use with the heterodyne detector of apparatus21. Theoutput of the keyed amplifier is, fed to a highly selectiveamplifier system 29. before being passed on to a final detector andsubsequently to the audio'amplifier stages 30 (shown conventionally inbox form). In order to quench or blockv the, receiver, there is provideda motor 20 similar to the motor shown at the transmitter and which isdriven in exact synchronismwith the motor at the transmitter over asimilar arrangement of crystal oscillator 22 and frequency divider 2|.The crystal-oscillators and frequency dividers at both the transmitterand receiver are designed to have the same constants. The motor 20serves to periodically quench or block the receiver in keyed amplifier28, which is ahead of the highly selective amplifier circuit. In thearrangements just described, the receiver blocking or quenching is doneahead of those circuits which effectively contribute to the receiverselectivity, in which case it will be seen that signal and noise energydelivered to the selective circuits will be only that which existsduring the short time periods when the receiver is not blocked and theseperiods are made synchronous with reception of transmitted pulses. Withsuch a condition, the signal and noise both have an equal chance atbuilding up energy in the circuits of the receiver until near the end ofthe transmitter on period, at which time the blocking at the receivercuts oil the noise while no signal energy is being received. Under thesecircumstances, the mean signalto-noise ratio is directly proportional tothe instantaneous transmitter power. No noise is permitted to build "upenergy in the selective circuits of the receiver except that whichexists while the receiver circuit is"open, which is the period duringwhich the signal makes its greatest impression; In order to obtainoptimum signalto-noise ratio, it is important that the circuits feedingthe selective circuits of the receiver be quenched no later than the endof the transmitter pulse period. Also, it is important that the receivernot be turned on or made receptive before the beginning of thetransmitter pulse period. Although power Of both signal and noise isdelivered to the selective circuits in pulses, the circuits do notfollow the pulses in amplitude but instead maintain a more or lessconstant energy level corresponding to the average power of pulse andspace periods. The selective circuits smooth out or suppress the pulsesbut are so designed as to respond to modulation frequencies lower thanthe pulse frequency, The transmitter power may then be amplitude, phaseor frequency modulated or keyed by useful signals, and these signalswill be reproduced in the receiver output with improved signal-to-noiseratio if the final receiver detector is suitably chosen.

In those cases where the instantaneous transmitter power lies above thenoise power, at the receiver, the improvement in signal tonoise ratiomay be obtained with a simpler arrangement at the receiver than thatshown in Fig, 3. The keyed amplifier may be replaced by an amplifier sodesigned and adjusted as to provide for a threshold effect. That is, theamplifier may provide output only when it is supplied with an inp t'grater than some fixed value, whi h may be the noise level, but less thanthe signal level. By this means all noise present between signal pulsestends to be supp e e A h u h existing f equ n y tandards are so ood thatsynchronism between transmitter pu ses and receiver quenching may bemaintained for long periods, I contemplate providing manual or automatictiming correction at the receiver in ways a ready well known infacsimile and television communication systems.

It is to be understood that the invention 15.1101 limited to the precisecircuit arrang ments illustratedand described, since variousmodifications may be made without departing om the spirit and scopethereof. As anv example, at the transmitter, in order to relieve theinstantaneous load on the transmitter during on-off telegraph keying atthe beginning of each dot and dash, the line sections betweenthetransmitter l and the half wave resonant line 4 may be madeonequarter of a wavelength long instead of one-half. wave length (shownin Fig. 1). By using one-quarter wavelength connections, the load on thetransmitter will be small at the beginning of each dot or dash and thenwill increase to normal as the energy is built up in the one-halfwavelength resonant line 4.

Also, the mechanically rotating pulsing equipment of transmitter andreceiver may be replaced by suitable electronic or gas dischargedevices. Suitable electronic and gas discharge equipment is alreadyavailable for use at the receiver and will be found in existingfacsimile and television equipment.

Itshould also be understood that, while I have illustrated the inventionas applied to a radio communication system, it is equally applicable toany other system, including" communication overcables, by supersonicmechanical waves, etc.

What is claimed is:

1. The method of operating a, radio system which includes producingalternating current energy of a predetermined frequency, continuouslystoring said alternating current energy of said frequency at a radiotransmitter and radiating the stored energy without change of frequencyfrom said transmitter for short time periods compared to the intervalsbetween radiating periods, thereby increasing the maximum power outputof the transmitter during radiation above the input power, andsynchronously controlling the receiver to be operative substantiallyonly during the radiation periods of the transmitter.

} 2. A radio system having a transmitter arranged to store upalternating current energy and to radiate periodically pulses of storedenergy for time periods short compared to the time intervals betweenradiated pulses. and a receiver arranged to be receptive substantiallyonly during the radiation periods of said transmitter.

3. A radio system having a transmitter and a remote receiver, meansatsaid transmitter for storingup energy and for radiating periodicallypulses of, stored energy for time periods short compared to the timeintervals between radiated pulses, said means including a motor, meansat said receiver including a motor for causing said receiver to beoperatively receptive substantially only during the radiation periods ofsaid transmitter, and means for synchronizing the Speeds of both motors.

4. A communication system comprising a transmitter having means forstoring energy and for transmitting pulses of energy for time periodsshort compared to the time intervals between transmitted pulses andrepeated at a rate higher than the highest useful modulation frequency,and receiving means responsive substantially only during periods ofarrival of transmitted pulses.

5. A communication system comprising means for delivering energycontinuously to an energy storage circuit, means for transmitting energytaken from the circuit in theform 01' pulses short compared to the timeintervals'between pulsesyand receiving means responsive substantiallyonly during periods of arrival 01 pulses.

6. A radio system having a transmitter for storing energy and forradiating pulses of stored energy which are short compared to the timeintervals between pulses, there being means at said transmitter formodulating said energy in accordance with useful signals, and a receiverarranged to be receptive substantially only during the periods ofarrival of said pulses, said receiver having means for demodulating thereceived pulses.

7. A system in accordance with claim 6, wherein the means at thetransmitter modulates the amplitude of the transmitter energy, and saidreceiver reproduces the signals.

8. A system in accordance with claim 6, where in the means at thetransmitter modulates the phase of the transmitter energy and saidreceiver reproduces the signals.

9. A system in accordance with claim 6, wherein the means at thetransmitter modulates the frequency of the transmitter energy, and saidreceiver reproduces the signals.

10. A system in accordance with claim 6, wherein the means at thetransmitter keys the transmitter energy, and said receiver reproducesthe signals.

11. A radio system having a transmitter for storing alternating currentenergy and for radiating a constant number of short duration pulses ofthe stored energy per second, and means for modulating a characteristicof said energy in accordance with desired signals, and a receiver forreceiving and demodulating said wave energy, said receiver having meansfor rendering said receiver insensitive to incoming waves duringsubstantially the entire interval between each pair of incomingsuccessive pulses.

12. A radio system having a transmitter for storing alternating currentenergy and for radiating a constant number of short duration pulses ofthe stored energy per second, and means for modulating a characteristicof said energy in accordance with desired signals, and a receiver forreceiving and demodulating said wave energy, said receiver having meansfor reducing the output of said receiver due to input to it during theintervals between incoming pulses.

13. A radio system having a transmitter arranged to store up energy andto transmit periodically pulses of stored energy for time periods shortcompared to the time intervals between transmitted pulses, and areceiver arranged to be receptive substantially only during thetransmission periods of said transmitter.

14. A transmitter including a power storing circuit composed of a tank,means for feeding in power to said tank at a uniform rate, and means forabstracting power intermittently from said tank and at a power ratewhich is substantially equal to the rate of storing multiplied by theratio of the pulse periods to the duration of the pulse, and a receiverarranged to be receptive substantially only during time periods when thetransmitted energy is arriving.

15. In a transmitter, an energy storage circuit, means for storingenergy in said storing circuit, and means for periodically utilizing thestored energy for very short time periods compared tothe time intervalsbetween them, and a receiver arranged to be receptive substantially onlyduring time periods when the transmitted energy is arriving.

16. The method of operating a radio system which includes continuouslystoring oscillatory energy at a radio transmitter and radiating thestored energy from the transmitter for short time periods compared tothe intervals between radi-, atingperiods, thereby increasing themaximum power .outputdn the transmittenduring, radiation:a l)ove theinput power, and synchronously controlling the receiver to beperiodically opera tive for receiving the energy radiated by saidtransmitter during the time periods whenthe transmitted energyisarriving at the receiver. H

17.,The method of operating a radio system which includes continuouslystoring energy at aradio transmitter and radiating the stored en: ergyfrom said transmitter for short time periods compared to the I intervalsbetween radiating pe-' riods, thereby increasing the ,maximum poweroutput of the transmitterduring radiation above the input power, andsynchronously controlling ,the receiver to be operative, substantiallyonly for delivering alternating currentenerg'y con-H tinuou'sly' to anenergy storagecircuit, means for transmitting energy "taken from thecircuit in theform of pulses short compared to the 'time intervalsbetween pulses, and receiving means responsive substantially only duringperiods of arrivalpf pulses.

.fZOIAQradio system having a 'transmitter am ranged to storeup..alternating' current energy and to transmit periodically, pulses ofstored en'- ergy for time periods shortcompared to the time intervalsvbetween transmitted pulses, and a receiverfarranged to be receptivesubstantially only duringfthe transmission periods'of said transmitten I21.. In a transmitter, an energy storage circuit, means for storing.alternatingcurrent energy in said storing circuit, and meansff orperiodically utilizing the stored energy ,f or very short time' periodscompared to: the time intervals between them; and a receiver aranged tobe receptive substantially only during time periods when thetransmittedener y is arriving.

-.-;22,=.Aradio systemhhaving a transmitter for storing alternatingcurrent energy, and for radiating a constant number of short durationpulses ofthe stored energy per 'second,..and means for modulating acharacteristic of said energy in accordance with desired signals, saidpulse frequency being'higher than, said modulation fre quency, and areceiver for receiving and demodulating said wave energy, saidreceiverhaving means for rendering said receiver insensitive to incomingwaves during substantially the entire interval between each pair ofincoming successive pulses.

23. A radio system having a transmitter for storing energy and forradiating short duration pulses of stored energy, and means formodulating a characteristic of said energy in accordance with desiredsignals, said pulse frequency being higher than said modulationfrequency, and a receiver for receiving and demodulating said waveenergy, said receiver having means for rendering the receiveninsensitive to incoming waves (ill during time intervals lying betweenincoming successive pulses, l

.24. A radio system having. a transmitter for storing energy-andforradiatingpulses of stored energy whichareshort compared ,tothe timeinterval between pulses, there being means at said transmitter formodulating said energy in accordance with useful signals, .and areceiver arranged to be non-receptive ,duringtime periods betweenthearrival of successive pulses, said receiverhaving .meansfordemodulating .the receivedpulses. a 25. A radio system, having atransmitter for storing energy and for radiating pulses of stored energywhich areshort compared to the time in-- terval,between.pulses,-there,being means at said transmitter for modulatingsaid ,energyin accordance .with;,useful signals,.and a receiverarranged; to be non-receptive during; time periods between the, arrivalofsuccessive-pulses. 26.A radio system having a transmitter for storingenergy and for radiating aconstant numberof short duration pulsesof thestored energy per second, and. means for modulating a characteristicofsaid energy in accordancewith desired signals, and .a receiver, forreceiving. anddemodulating said wave energy, said receiver having means.for rendering said receiver insensitive to incoming waves during atime'period lying between eachpair of incoming successive pulses.

;2 '7.-A:.transmitter including a power storing circuit composed; ofatank, means forfeeding in power to said tank, at ,a uniform rate, andmeans forabstracting power intermittently from said u tank-land at apower rate which issubstantially equal to the rate of storing.multiplied by the ratioof the pulse periods to the duration of thepu1se,;and-a receiver arrangedto be non-receptiveduring time periods,lying between time periods whenithe transmitted energy isarriving.

, 28..Ina pulse: communication system,;a ,receiver for receiving'signalstransmitted, by pulses which are very short compared to the timeintervalsbetween them, comprising an energy input circuit, a receiver.coupled to said input circuit, and 1means forpreventing energy.collected. by said, input circuit solely during substantially theentire time periods between received signal pulses fromcausing aresponsein the output of.

the receiver.

129. A receiving system for receiving message waves transmitted by;pulses which areshort compared to the time intervalsibetweenthem andwhich are sentout from-a remotely located transmitter, comprising anantenna,a keyed amplifier, means for keying said: amplifier at thefrequency ofthe received pulses, broadly selective circuits onlyincluding a-detector-coupled between said antenna andthe input of saidamplifier, a-relatively narrow band selective circuit coupled to theoutput of said keyed amplifier, a utilization circuit coupled to saidnarrow band selective circuit, whereby energy received by said antennaduring periodically repeated selected time periods is prevented fromcontributing to the output of said receiving system.

collecting device to said keyed amplifier without destroying the pulsewave form, means for keying said amplifier to make it responsive at timeintervals repeated at the pulse rate, synchronizing apparatus for saidmeans, and a highly selective amplifier coupled to the output of saidkeyed amplifier.

31. A single channel receiving system for re ceiving message wavestransmitted by pulses which are short compared to the time intervalsbetween them and which are sent out from a remotely located transmitter,comprising an energy collecting device, a keyed amplifier, circuitsincluding a heterodyne detector coupling said keyed amplifier and saidenergy collecting device and all designed to pass pulse energy from saidcollecting device to said keyed amplifier without destroying e pulsewave form, means for keying said amplifier to make it responsive at timeintervals repeatedat the pulse rate, and a highly selective amplifiercoupled to the output of said keyed amplifier, and a final detectorcoupled to the output of said highly selective amplifier.

32. In a pulse communication system, a receiver for receiving signalstransmitted by pulses which are very short compared to the timeintervals between them, comprising an energy input circuit, a receivercoupled to said input circuit, selective circuits for said receiver, andmeans for preventing energy collected by said input circuit solelyduring substantially the entire time periods between received signalpulses from. aflecting the selective circuits of said receiver.

33. In a pulse communication system, a transmitter for sending outpulses of high frequency energy which are short compared to theintervals between pulses and whose peak power is increased by an amountsubstantially equal to the ratio which the time interval between pulsesbears to the time duration of the pulses, means at said transmitter formodulating a characteristic of said high frequency energy in accordancewith the intelligence to be conveyed, a receiver having means forrendering certain circuits thereof insensitive for substantially theentire time period between received pulses and no later than the end ofthe transmitter pulse period.

34. A system for the reception of power transmitted in the form ofpulses which are short compared to the time between pulses and whichcarry intelligence, comprising means for delivering pulse power to anenergy storage circuit during substantially all of each pulse timeperiod but substantially only during the time periods when thetransmitted pulse power is arriving.

35. A system for receiving message waves transmitted by series of pulseswhich are short compared to the time between pulses and which aremodulated by the intelligence to be conveyed, comprising means fordelivering power to a frequencyselective circuit only during timeperiods of arrival of pulses, but during substantially all which pulsesare short compared to the time periods between transmitted pulsescomprising means for interrupting the operation of a portion of thereceiver during substantially the entire time periods between receivedpulses except for those periods during which the received pulses arrive.

37. A receiver for receiving signals transmitted in the form of carrierwave pulses which are short in comparison with the maximum timeperiodsavailable for the pulses and whose carrier wave is modulated bythe intelligence to be conveyed, comprising means for interrupting theoperation of portions of the receiver during, but only during, timeperiods not occupied by said carrier wave pulses.

38. A radio system having a transmitter for storing energy and forreleasing said energy in the form of pulses of alternating currentenergy of increased power level, and a receiver having means thereatoperating in synchronism with said transmitter for effectively renderingit nonreceptive during time periods between the arrival of said pulses.

39. A radio system having a transmitter for storing energy and utilizingsaid stored energy to produce pulses of high frequency energy to beradiated by said transmitter, there being means at said transmitter forimpressing modulations on the pulses of high frequency energy to beradiated, and a receiver arranged to be non-receptive during timeperiods between the arrival of successive pulses, said receiver havingmeans for demodulating the received pulses.

40. The method of operating a radio system which includes continuouslystoring radio frequency energy at'a radio transmitter and radiating thestored energy, without change of frequency, from said transmitter forshort time periods compared to the intervals between radiating periods,thereby increasing the maximum power output of the transmitter duringradiation above the input power, and synchronously controlling thereceiver to be operative substantially only during the radiation periodsof the transmitter.

41. A communication system comprising a transmitter having means forstoring output cur- I rent energy and for transmitting pulses of thisenergy, without change of frequency, for time periods short compared tothe time intervals between transmitted pulses and repeated at a ratehigher than the highest useful modulation free quency, and receivingmeans responsive substantially only during periods of arrival oftransmitted pulses.

CLARENCE W. HANSELL

